The present invention relates to a heating apparatus for automobiles, or more in particular to an electric heating apparatus for automobiles, using automobile electric power supplies in such a manner that a comfortable heating effect is attained at low temperatures of the engine cooling liquid immediately after starting the automobile engine.
A construction of a heating apparatus is known in which an electric heat generating member is arranged in a ventilation circuit of a hot-water type heating apparatus using the engine cooling liquid as a heat source thereby to supply hot air into the automobile passenger space until the engine cooling liquid is heated to such a degree that the air temperature reaches a predetermined value. In particular, the heat generating member comprises an element of semiconductor ceramics having a positive temperature coefficient of resistance (PTC) characteristic so that when the temperature of the air flowing in from the hot water type heating apparatus and circulating in the ventilation circuit increases to a predetermined value, the heat source is switched automatically from the heat generating member to the hot-water type heating apparatus by the self-control of the temperature of the heat generating member. In other words, the prior art relates to the function of the heat generating member itself.
In the above-mentioned construction of the conventional heating apparatuses, it is possible to start heating as soon as the engine starts. In actual applications, however, practically comfortable heating requires an amount of heat from the heat generating member which meets the thermal capacity of the whole of the automobile cabin. Thus an additional electric power consumption is required from the electric power supply, and therefore it is necessary to provide a power supply capacity for achieving the object of the prior art when the heat generating member is operated. The amount of the power required for the comfortable heating, on the other hand, is very great as compared with the power supply capacity, thus making it inevitably necessary to increase the capacity of heat generation as much as possible.
Such a consideration is overlooked in the construction of the conventional heating apparatuses. Specifically, the prior art constructions are such that the user is always afraid of a decreased capacity of the battery and an inability to restart the engine at the sacrifice of the heating capacity. Further, the over-discharge of the battery shortens the service life thereof, thus reducing the function thereof as a power supply for other equipment. Furthermore, in spite of the fact that the heat generating member utilizes the Curie point of a positive resistance temperature element and therefore it is possible to switch the heat source to the engine cooling liquid automatically, the Curie point is required to be as low as 75.degree. to 85.degree. C., with the result that the heat exchange ability requires an increased effective area of the heat generating member, thus making the apparatus inconveniently bulky for practical purposes.